1. Field of the Invention
This invention relates to a high-speed imaging stage that is capable of continuous and high-speed imaging on radiographic recording materials including stimulable phosphor sheets and X-ray films.
2. Prior Art
Radiation imaging has conventionally been accomplished by radiographic systems that use a sensitizing paper in combination with a radiographic film having an emulsion layer that is made of a silver halide light-sensitive material. Recently, a system for recording and reproducing radiation information using stimulable phosphor is drawing increasing attention from researchers as a promising substitute for radiographic systems.
Certain phosphors, when exposed to radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, electron beams and ultraviolet rays, store part of the energy that the radiation possesses. When the phosphor is subsequently exposed to excitation light such as visible light, it produces stimulated emission corresponding to the stored energy. The phosphor exhibiting such properties is known as a stimulable phosphor.
Various systems have been proposed for recording and reproducing radiation images using stimulable phosphor. In those systems, the radiation image of a subject such as the human body is first stored in a sheet having a layer of stimulable phosphor (which is hereinafter referred to simply as a "phosphor sheet") and the sheet is then scanned with excitation light to produce a stimulated emission. The stimulated emission is read with an optical device to obtain electrical image signals, which are subsequently processed to produce a radiation image of the subject that is sharp enough to insure accurate diagnosis (see, example, Japanese Patent Application Kokai Nos. 12429/1980, 11395/1981, 163472/1980, 104645/1981 and 116340/1980).
The phosphor sheet is not intended to store the image information permanently but it is merely used to retain radiation image information temporarily before a final image is formed on a recording medium. Hence, the phosphor sheet may be designed to be used cyclically. This is not only very economical but also convenient.
In order to form radiation image on the phosphor sheet in the radiation image information recording and reproducing system described above, a subject such as the human body and the phosphor sheet are placed in specified positions in the imaging (recording) apparatus and the radiation emitted from a radiation source such as an X-ray source is applied to the phosphor sheet through the subject.
In examining the circulatory system of the human body as well as checking the functions of various organs, a contrast medium is injected into blood vessels and the state of blood circulation is investigated. For accurate diagnosis, the part of interest must be imaged continuously at high speeds of 2-6 pictures per second depending on the speed of blood circulation. To meet this need, various types of high-speed imaging stages that are capable of high-speed continuous imaging and that hence are adapted for imaging the state of blood circulation and other phenomena, have been proposed and commercialized for use with the systems of recording and reproducing radiation image information.
As already mentioned, radiation image information is recorded on the phosphor sheet by illuminating it with radiation through the subject to be imaged. In this case, the time of exposure of the phosphor sheet to radiation, namely, the time required for imaging, is usually very. In order to achieve high-speed continuous imaging at speeds of 2-6 pictures per second, it is important that the phosphor sheet be ejected as soon as possible after imaging and that additional phosphor sheets be supplied to predetermined positions as rapidly as possible.
One of the conventional high-speed imaging stages that have been proposed to meet this requirement is described in commonly assigned Japanese Patent Application Kokai No. 200248/1985. An engaging member is provided both at the position where phosphor sheets are subjected to imaging and at the position where they, are accommodated following ejection after imaging. The phosphor sheets are moved at high speed, either with air or by various mechanical means using an urging member, so that they impinge against the engaging members at the specified positions for supply and ejection. However, in this method, the phosphor sheets are supplied to the specified position at a high speed until they impinge against the engaging member and, therefore, the expensive phosphor sheets are damaged so heavily that they become unsuitable for use in a very short period of time, thereby making it impossible to use them cyclically in the economical manner already mentioned above.
The assignee also proposed in Japanese Patent Application Kokai No. 104936/1985 a method of performing imaging on phosphor sheets that are individually placed within protective cases. However, this method is incapable of rapid diagnostic imaging since it takes time to place the phosphor sheets individually into separate protective cases.